Referring to FIG. 10, it is known to provide an electrically-operated, in-tank fuel pump 100. Pump 100 includes a main pump housing 102 and an end cap 104. It is common to equip electrical pumps of this type with a brush type (e.g., DC) electric motor. End cap 104 includes a fluid outlet 106 for outputting the flow of pumped fuel, and an electrical connector 108 that includes a pair of electrical terminals configured for connection to an external wiring harness, for example. The electrical terminals of the connector 108 are typically used for providing positive and negative polarity DC voltage to the pump to energize the electric motor. The DC voltage across the positive and negative terminals is subsequently applied via a pair of DC motor brushes to a motor armature or the like. The DC motor brushes (not shown in FIG. 10) are typically spring-biased to allow for movement during the operating life of the pump 100 (i.e., to maintain a positive contact as the brushes themselves wear out). In view of this, it also known to provide a pair of so-called flexible shunt wires, which may be braided wires, to connect each of the electrical terminals to its respective brush. However, when the pump 100 is used in high alcohol content based fuels or other fuels with increased electrical conductivity, the flexible shunt wires are subject to, and in-fact experience, degradation. In particular, electrolysis of the positive shunt wire causes metal loss, which may ultimately result in an open circuit condition, causing a failed fuel pump.
FIGS. 11-13 show one approach taken in the art to address this problem, with FIG. 11 being a top view and FIGS. 12 and 13 being cross-sectional views taken substantially along lines 12-12 and 13-13 in FIG. 11, respectively. This approach calls for protecting the shunt wires from electrolysis by arranging the brushes with axial shunt wires that are contained in the same bore that houses the motor brush (i.e., are isolated within the brush bore and thus electrically isolated from the other, opposite polarity shunt wire/terminal). FIG. 13 shows a pair of bores 110 with respective brushes 112 and shunt wires 114. By creating a high resistance electrical path between the anode and cathode, any adverse effect of electrolysis is minimized. However, the axial shunt design is undesirable due to the difficulty in integrating the shunt wire into a radio frequency suppression circuit. For example, a common RFI circuit includes a coil and ferromagnetic core assembly, which in this conventional approach would have to occupy the same axial space as the springs that bias the brushes. Accordingly, for axial shunt wire designs, it is common to include a secondary RFI module 116 and electrical connector, offset from axial alignment, as required to accomplish this function, as seen in FIG. 12.
FIGS. 14-15 show another approach taken in the art, namely, a side-connected shunt wire design. FIG. 14 is a partially broken away side view of an end cap showing an electrical terminal 118, a first end 120 of a coil 122, a second end 124 of the coil 122, a core 126, a flexible shunt wire 128 and a side-mounted connection 130 to brush 132. A desirable method to integrate the brush 132 and shunt wire 128 into an radio frequency interference (RFI) suppression circuit is to use a side shunt design that provides for the shunt wire attachment directly to the RFI circuit (i.e., coil and core) in a design that integrates the brushes, RFI circuit and electrical terminals all in one brush carrier or end cap assembly. However, this known method provides no electrical isolation between the opposite polarity shunt wires, as would be needed to minimize or prevent electrolysis. FIG. 15 shows a positive polarity shunt wire 134, a negative polarity shunt wire 136 and a path 138 through which electrolysis proceeds in the presence of an electrically conductive fuel.
There is therefore a need for a fuel pump end cap assembly that minimizes or eliminates one or more of the problems set forth above.